Decaying compressible turbulence with thermal non-equilibrium

摘要

The interaction of decaying turbulence with thermal non-equilibrium (TNE) is studied using direct numerical simulations. The focus is on energy exchanges and decay rates in decaying flows with initial vibrational excitation. A key finding is the identification of different regimes in the interaction and the nondimensional parameter (beta) that controls it. The latter accounts for the degree of initial TNE as well as the ratio of timescales of turbulence and vibrational relaxation. For beta 1, TNE is essentially frozen and turbulence is largely unaffected by the decay of vibrational energy. For beta 1, TNE relaxation is relatively fast and produces an increase in translational-rotational energy, which, through changes in transport coefficients, leads to a temporary increase in dissipation leading to faster turbulence decay rates. Theoretical arguments are put forth to determine the asymptotic limits of this effect. TNE relaxation is also affected by turbulent fluctuations in unexpected ways. For example, although initial conditions are always vibrationally hot, the flow may undergo vibrationally cold transients, which are explained through simple models. The results presented here help explain disagreement between previous experimental and numerical data.